1. Field
The present invention relates to an organic light emitting device and a method for manufacturing the same.
2. Description of the Background Art
Organic Light emitting device (OLED) refers to a device for injecting electrons and holes from an electron injection cathode and a hole injection anode into a light emitting layer, respectively, and emitting light when excitons, which are combinations of the injected electrons and holes, are transited from an excited state to a ground state.
The organic light emitting device is classified into a Passive Matrix Organic Light emitting device (PMOLED) and an Active Matrix Organic Light emitting device (AMOLED) depending on its driving method. A thin film transistor for driving the active matrix organic light emitting device is classified into several kinds depending on its forming method and material, such as amorphous silicon (a-Si) and polycrystalline silicon (p-Si, Low Temperature polycrystalline Silicon: LTPS).
The active matrix organic light emitting device using a polycrystalline silicon thin film transistor has a disadvantage that its cost competence is very low compared with the a-Si.
The active matrix organic light emitting device using an amorphous silicon thin film transistor has an excellent cost competence compared with the p-Si, but has a disadvantage that a cathode should connect with a source or drain electrode and an organic light emitting diode should be inversely formed since the active matrix organic light emitting device is of a source type.
A drawback of the conventional organic light emitting device will be described with reference to FIGS. 1A and 1B.
FIG. 1A is a cross-sectional view illustrating conventional organic light emitting device. FIG. 1B is a cross-sectional view illustrating organic layer of conventional organic light emitting device of FIG. 1A.
As shown in FIGS. 1A and 1B, in the conventional organic light emitting device 100, a thin film transistor 130 and a light emitting diode 140 are formed on a substrate 110. A passivation layer 160 is formed and covers the thin film transistor 130 and the light emitting diode 140. A cover substrate 120 is provided and protects a device formed on the substrate 110. The substrate 110 and the cover substrate 120 are sealed using sealant 170. When the organic light emitting device 100 is a top emission type, the cover substrate 120 is formed of transparent glass.
In detail, a gate electrode 131 is formed on the substrate 110 and a gate insulating layer 132 is formed on the substrate 110 comprising the gate electrode 131. An active layer 133 is formed of amorphous silicon on the gate insulating layer 132. Ohmic contact layers 134 are formed on both sides of the active layer 133. A source 135 and a drain 136 are formed on the ohmic contact layers 134, thereby constituting the thin film transistor 130.
A planarization layer 150 is formed on the thin film transistor 130 so that a light emitting diode 140 can be formed uniformly over the thin film transistor 130. The planarization layer 150 has a contact hole for electrically connecting the underlying thin film transistor 130 with light emitting diode 140. A cathode 141 is formed on the planarization layer 150, and connected with the drain 136 of the thin film transistor 130 through the contact hole.
An Organic layer 143 is formed on the cathode 141, and an anode 144 is formed on the organic layer 143, thereby constituting the light emitting diode 140. The light emitting diode 140 emits light by driving the thin film transistor 130. As shown in FIG. 1B, the organic layer 143 comprises an emission layer (EML) 143c formed of an organic material and further comprises a hole injection layer (HIL) 143e and/or a hole transport layer (HTL) 143d between the emission layer 143c and the anode 144, an electron transport layer (ETL) 143b and/or an electron injection layer 143a (EIL) between the emission Layer 143c and the cathode 141. The organic layer 143 is formed on a portion of the cathode 141 exposed by the insulating layer 142.
In the above organic light emitting device 100, the light emitting diodes 140 should be all formed inversely (generally, in case of inverted top type) because the thin film transistor 130 comprises amorphous silicon layer. In general, the cathode 141 is formed of aluminum (Al). It is difficult to apply the aluminum (Al) to a device because oxide is generated when the cathode 141 is patterned by photolithography process or deposited under atmosphere.
Therefore, in an alternative manner, after forming a metal layer for the cathode 141 under vacuum, the organic layer 143 is formed on the metal layer for cathode 141 under vacuum and directly, and the cathode 141 is formed by the pattering the metal layer. Then, there occurs a drawback that it is impossible to form the cathode pattern.
In addition, in case of inverted top type OLED, the anode 144 is formed using a thin metal layer or a conductive material (Indium Tin Oxide: ITO). In this case, there occurs a drawback that the organic layer 143 of the light emitting diode 140 is damaged when the anode 144 is formed by sputtering using conductive material.